Auto attendant or PBX attendant bypass systems are known in the art for automatically connecting an outside caller through a telephone company central office to an extension of a telephone switching system such as a private branch exchange (PBX), key telephone system or centrex system. An example of such an auto attendant system is given is U.S. Pat. No. 4,696,028, incorporated herein by reference.
In one known form of an auto attendant system, the auto attendant is interposed between the telephone central office serving the called party's business or institution and the switching system serving that same business or institution. In this embodiment, the auto attendant system uses port circuits, either of the normal station type or of the Direct Inward Dial (D.I.D.) type to connect the auto attendant to the switching system. Also, in this embodiment, one-way, trunk. circuits are required.
In a second known form of an auto attendant system, the auto attendant is not directly connected to the telephone company central office, but is connected only to station circuits of the switching system. In this embodiment, the auto attendant depends on incoming calls being routed to it by a common PBX feature sometimes known as Direct In-Line or Direct Department Calling. This feature requires that the auto attendant further use the switching system transfer capabilities in order to extend the call to the inside party selected by the outside party. The use of the conventional switching system transfer capability requires the use of a switch hook flash to alert the switching system that a call transfer is desired. Subsequent to the switchhook flash the outside party is placed on "hold" for varying amounts of time and normal call progress tone indications (such as ringback tone) may not be heard by the caller. Further, in some PBX systems, specialized transfer or conference circuits are automatically assigned by the switching system, therefore requiring additional provisioning of such specialized circuits when an auto attendant is used according to this second method.
There therefore exists a need to bring auto attendant functionality to business or institutional users of switching systems without the limitation of the above described conventional methods.
Many switching systems are equipped with a direct inward system access (DISA) feature. The DISA feature is designed to allow an authorized outside caller to make long distance calls and have them billed to the telephone number associated with the switching system. Such DISA features may also allow the authorized outside person to dial extension numbers of inside personnel and to be connected to such extensions. When a person desires to use the DISA feature, he or she calls a special number of the switching system. The caller hears ringback tone followed by a dial tone (this dial tone would normally confuse a naive caller not knowing what a dial tone meant after a ringback tone). An authorized person then inputs a secret security code. After the reception of this code, the authorized person may make an outgoing long distance call and have the call billed to the business, and specifically to an account associated with the secret code.
The present invention satisfies a need for enhanced access into PBX systems without providing special communication lines by using the DISA feature in combination with existing PBX trunk circuits.